1. Technical Field of the Invention
The present invention relates to a functional device having a photoelectric conversion layer or a luminescent layer over a substrate in a deposited state.
2. Description of the Related Art
Functional devices using organic materials, notably organic luminescent devices, have made remarkable progress in recent years. And an organic EL display as a representative of organic luminescent devices has had a success in practical utilization. On the other hand, a photoelectric conversion device as an example of functional devices, though not yet successful in manufacturing, has made considerable strides in recent years, and has the potential to overcome problems facing the related art imaging devices, which are mentioned below. A related art solid-state imaging device, whether a CCD type or a CMOS type, includes a semiconductor substrate on the surface of which are formed a large number of photoelectric conversion devices (photodiodes) to function as light-receiving portions and signal readout circuit for reading out photoelectric conversion signals obtained from each photoelectric conversion device. The signal readout circuit is made up of charge transfer circuit and transfer electrodes in the case of CCD type, while it is made up of MOS transistor circuit and signal wiring in the case of CMOS type.
Therefore, the related art solid-state imaging devices require forming a great number of light-receiving portions and signal readout circuit on the surface of one and the same semiconductor substrate. So there is a problem that a sufficiently large area cannot be allocated to the light-receiving portions. Since the light availability of a solid-state imaging device is greatly reduced so far as a large area cannot be allocated to its light-receiving portions, light availability shortage in related art solid-state imaging devices has been supplemented by mounting microlenses or inner lenses on the upper parts of light-receiving portions and focusing light through these lenses onto the light-receiving portions. However, such a measure has inevitable problems including an increase in light quantity loss due to optical reflection, so it is said that the existing imaging devices have several tens of percentages of light quantity loss. In addition, the fineness requirements for solid-state imaging devices are becoming severer from year to year, and progress toward fining light-receiving portions leads to a problem that an incident light angle differential between the periphery and the center of an imaging device causes differences in light-gathering rates of microlenses to result in a shading phenomenon.
Therefore, opinions on the solid-state imaging device structure disclosed in JP-A-58-103165 have been changed for the better. This solid-state imaging device has a structure that signal readout circuit formed on the surface of a semiconductor substrate is deposited with photosensitive layers, and these photosensitive layers act as photoreceptor members and photoelectric conversion signals from these layers are taken out by the signal readout circuit, that is, a structure of photoelectric conversion layer-stacked type.
Such a structure can secure a large light-receiving area, and makes it possible to solve the aforementioned problem. Of late the solid-state imaging devices of photoelectric conversion layer-stacked type were proposed in JP-A-2002-83946, JP-T-2002-502120, JP-T-2003-502847 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application), and Japanese Patent No. 3,405,099. Application of an organic material-utilized device to the photoelectric conversion layer of the foregoing structure is highly desirable from the following viewpoints. It is relatively easy to adjust spectral wavelengths of organic materials by changing their chemical structures, and besides, the photoelectric conversion layer using an organic semiconductor can achieve a thickness of the order of 100 nm, so the total thickness can be held down even when a plurality of layers are deposited.
However, formation of functional devices by use of organic materials requires patterning electrodes on the functional layers, and fine patterning according to methods hitherto adopted suffers a problem that the devices formed deteriorate considerably in their performances. In the case of photolithographic processing in particular, there is a problem that since a development process after exposure is essential therein, purified water used for washing treatment in the development process reaches an organic semiconductor layer and degrades the organic semiconductor layer; as a result, there occurs a marked drop in device performance.
Further, organic material-utilized functional devices sometimes undergo deterioration from a migration of metals used in electrodes or wiring into adjacent layers, which is caused by an electric field applied to the electrodes between which organic layer is sandwiched and to the wiring under operation. In the case of photofunctional devices in particular, such as luminescent devices and photoreceptive devices, minimization of the area of contact regions is favorable for an increase in light-receiving area because the contact regions become light-screened regions. However, when the migration as mentioned above occurs in the minimized contact regions, contact performance is lowered and device functionality is substantially reduced.
Although metal oxides such as ITO are in the mainstream of conductive materials widely used as light-pervious electrodes in photofunctional devices, such metal oxide-utilized devices have a problem that the immediate contact between metal oxide and aluminum traces causes reaction between the oxygen and the aluminum to result in considerable decrease of contact performance.